The changing shape of the U.S. population age structure will dramatically increase the number of osteoporotic fractures in the elderly; the increase will disproportionately affect minorities and men. It is therefore important to understand the epidemiology of osteoporosis in these populations. While there are clear racial/ethnic differences in fracture rates, their origins are not understood. The proposed study will be a comprehensive effort to further our understanding of the fundamental causes of racial/ethnic disparities in fracture rates by focusing on markers of two primary `upstream' determinants of fracture: falls and bone fragility. The Boston Area Community Health/Bone (BACH/Bone) Survey is a study of skeletal health in a randomly selected group of 1,219 black, Hispanic, and white men between 29-80 y. BACH/Bone staff have been very productive, producing over 10 papers for peer-reviewed journals. We propose a second wave of data collection on ~825 men to begin ~6.5 y after baseline, when the cohort will be between 35-86 y. The Specific Aims of the proposed study are to, in a racially/ethnically diverse, population-based sample of men: 1) Estimate longitudinal changes in markers of bone strength and fall risk, with and without adjustment for known risk factors; 2) Determine the relative contributions of social factors, individual risk behaviors and health status, and physiological influences to racial/ethnic differences in markers of fall risk and bone strength; 3) Establish the first age- and racial/ethnic group-specific, population-based estimates of bone microarchitecture, and identify determinants of observed age and racial/ethnic differences; 4) Determine whether there are age and racial/ethnic differences in the ratio of bone loads to bone strength (the `factor of risk'); 5) Examine whether genetic ancestry contributes to variations in markers of fall risk and bone strength beyond that attributable to self-identified race/ethnicity. The representativeness and racial/ethnic diversity of the BACH/Bone cohort are unique, and, as such, the potential impact of the study is enormous. By focusing upstream on markers of fall risk and bone strength with state-of-the-art measures, it will make landmark contributions to our understanding of the elusive mechanisms underlying racial/ethnic differences in bone fragility.